Conventionally, an evaporated fuel processing device is widely used. This evaporated fuel processing device is arranged to temporarily adsorb an evaporated fuel generated in a fuel tank of a vehicle to a canister using adsorption material (adsorbent) such as activated carbon, then to purge combustion components from the canister by introduction of flesh air during driving of the internal combustion engine, and to introduce it into an intake system of the internal combustion engine.
Japanese Patent No. 4107053 discloses an evaporated fuel processing device which includes a blocking valve provided in a passage between a fuel tank and a canister, and which is basically arranged to adsorb an evaporated fuel from the fuel tank in the canister only at a refueling. That is, a fuel tank is maintained in a sealed state by the blocking valve during a stop of the vehicle, except for the refueling. This is a system arranged to surely prevent outflow of the evaporated fuel to the outside.
The evaporated fuel processing device of the patent document 1 includes a diagnosis device arranged to diagnose whether or not there is a leakage of each portion. The diagnosis device of Japanese Patent No. 4107053 includes a negative pressure pump connected to a drain port side of the canister. The inside of the system including the fuel tank and the canister is depressurized by this negative pressure pump at an appropriate timing during the stop of the vehicle. The existence of the leakage is judged based on the pressure variation of the inside of the system at that time.
However, in this leakage diagnosis using the pump, the energy consumption according to the actuation of the pump is generated at each diagnosis.
On the other hand, Japanese Patent No. 4715426 proposes a leakage diagnosis performed by using a pressure variation within a tank by a difference between an outside air temperature and a fuel temperature after a stop of an engine, without using a pump.
However, a fuel tank of a sealed type which is used in an evaporated fuel processing device including a blocking valve generally has a large thickness and a rigid configuration. Accordingly, a variation of a fuel temperature by the outside air temperature is difficult to be obtained.